The prediction of the flexural lumber properties from standing South African-grown Pinus patula trees

Abstract

Pinus patula is the most intensively planted conifer in the tropics and subtropics. The increased proportion of corewood that results when rotation ages of pine plantations are shortened has become a wood quality factor of growing concern worldwide. The purpose of this study was to develop empirically based models for predicting the flexural properties of the wood produced from relatively young P. patula trees. Models were based on the properties of standing trees, and their effectiveness was evaluated at board, tree, and compartment levels. Sample material was obtained from 170 P. patula trees, 16–20 years old, established in 17 compartments on the Mpumalanga escarpment of South Africa. Multiple regression models were developed, which managed to explain 68, 60, and 95 % of the variation in the dynamic modulus of elasticity (MOE) on individual boards, trees, and compartments levels, respectively. At compartment level, 80 % of the variation in the 5th percentile MOR value could be explained by the model. Sensitivity analyses showed that site index at base age of 10 years, acoustic time of flight, wood density, and ring width were influential variables in the MOE models. The models indicated that tree slenderness during early growth seems to play a major role in determining the dynamic MOE and MOR of lumber. This is in agreement with Euler’s buckling theory and the bending stress theory. The results from this study indicated that the MOEdyn and MOR of lumber can be accurately predicted on especially a compartment level. The predictive models developed can be used as management tools to improve operational decisions around tree breeding, silvicultural practices, and rotation ages.